Field of the Invention
This invention relates to evaluation of a medical condition by analysis of electromagnetic signals. More particularly, this invention relates to improvements in detecting and measuring certain aspects of the electrocardio-graphic cycle.
Description of the Related Art
The meanings of certain acronyms and abbreviations used herein are given in Table 1.
TABLE 1Acronyms and Abbreviations3-D3-dimensionalLVLeft VentricleLBBBLeft Bundle Branch BlockECGElectrocardiogramMRIMagnetic Resonance ImagingLATLocal Activation TimeIC-ECGIntracardiac ECGWOIWindow of InterestFFFar FieldNFNear FieldIC-EGMIntracardiac ElectrogramsEGMElectrogram
Three-dimensional (3-D) images of internal organs are useful in many catheter-based diagnostic and therapeutic applications, and real-time imaging is widely used during surgical procedures.
Mapping of electrical potentials in the heart is now commonly performed, using cardiac catheters comprising electrophysiological sensors for mapping the electrical activity of the heart. Typically, time-varying electrical potentials in the endocardium are sensed and recorded as a function of position inside the heart, and then used to map a local electrogram or local activation time. Activation time differs from point to point in the endocardium due to the time required for conduction of electrical impulses through the heart muscle. The direction of this electrical conduction at any point in the heart is conventionally represented by an activation vector, also referred to herein as a conduction velocity vector, which is normal to an isoelectric activation front, both of which may be derived from a map of activation time. The rate of propagation of the activation front through any point in the endocardium may be represented as a conduction velocity vector.
Localized defects in the heart's conduction of activation signals may be identified by observing phenomena such as multiple activation fronts, abnormal concentrations of activation vectors, or changes in the velocity vector or deviation of the vector from normal values. Examples of such defects include reentrant areas, which may be associated with signal patterns known as complex fractionated electrograms. Once a defect is located by such mapping, it may be ablated (if it is functioning abnormally) or otherwise treated to restore the normal function of the heart insofar as is possible.
The document Characterization of Left Ventricular Activation in Patients With Heart Failure and Left Bundle-Branch Block, Auricchio et al., Circulation. 2004; 109:1133-1139 describes LV activation sequences in patients with heart failure and LBBB QRS morphology with simultaneous application of 3-D contact and noncontact mapping during intrinsic rhythm and asynchronous pacing. A “U-shaped” activation wave front was present in most of the patients because of a line of block that was located anteriorly, laterally, or inferiorly. Functional behavior of the line of block was demonstrated by a change in its location during asynchronous ventricular pacing at different sites and cycle length.